Off Idle Stumble When Cold
Thread Starter
Instructor
Joined: Mar 2002
Posts: 174
Likes: 1
From: Raleigh NC
Off Idle Stumble When Cold
I have a '72 convertible with a ZZ4 and a Holley Street Avenger 4 barrel. We just got the car back from the restorer and have noticed that when we pull away from a stop the car "stumbles" and stalls when cold.
Does anyone have an idea as to what the problem might be?
Many thanks
Does anyone have an idea as to what the problem might be?
Many thanks
Melting Slicks
Joined: Dec 2000
Posts: 2,041
Likes: 0
From: Wichita, KS
Re: Off Idle Stumble When Cold (Texaggie)
Yep. That's why we all love our newer fuel injected vehicles! If you work out the off idle stumble when the engine is cold you're going to cause other problems when the car is warm.
Burning Brakes
Joined: Oct 2001
Posts: 1,185
Likes: 0
From: New Wilmington PA
Re: Off Idle Stumble When Cold (Texaggie)
I had the EXACT same issue with my ZZ4 and it actually convinced me to go EFI. I never solved the stumble problems before the swap but I may have a little insight on the issue.
ZZ4 has no exhaust crossover so intake air is always cold. Great for the summer TERRIBLE for the winter.
You need a LOT more fuel to run an engine cold. (very rich mix) It may not be possible to provide a rich enough mix while cold without running rich when fully warmed. That said it MAY be possible too. After switching to EFI I found MONSTER vacuum leaks and believe that was contributing to my cold drivability issues.
Vacuum leak=leaner mix.
I would highly suggest testing the vacuum lines coming off the engine before attempting to adjust any mixture settings.
Good luck man! :cheers:
ZZ4 has no exhaust crossover so intake air is always cold. Great for the summer TERRIBLE for the winter.
You need a LOT more fuel to run an engine cold. (very rich mix) It may not be possible to provide a rich enough mix while cold without running rich when fully warmed. That said it MAY be possible too. After switching to EFI I found MONSTER vacuum leaks and believe that was contributing to my cold drivability issues.
Vacuum leak=leaner mix.
I would highly suggest testing the vacuum lines coming off the engine before attempting to adjust any mixture settings.
Good luck man! :cheers:
